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On-line analysis of the stability and other features of froths and foams by use of digital image processing

Ellis, Rene (2002-03)

Thesis (MScEng)--University of Stellenbosch, 2002.

Thesis

ENGLISH ABSTRACT: The objective of this study is the assessment of the usefulness of an industrial
machine vision system for laboratory studies of especially flotation froths and other
foams. With this in mind it was attempted to meet three objectives. The first objective
is the adjudication of the machine vision system's ability through image analysis to
differentiate between characteristics of two-phase and three-phase systems. Secondly,
through the use of image analysis the effect of varying surfactant concentration, as
well as the addition of quartz particles on the foam/froth stability was quantified and
thirdly it was attempted to define the nature of foam decay as stochastic or
deterministic. While not as important in the industrial setting, the last objective is
quite important when a laboratory system is concerned, even more so owing to the
difficulty of quantifying the collapse or decay of foams and froths.
Two experimental set-ups were used to attain above-mentioned objectives. A Leeds
flotation cell was used for the flotation of the quartz with cetyltrimethylammonium
bromide (CTAB) and octadecylamine (ODA) and as well as for the characterisation of
the CTAB and ODA foam. A glass column was used to investigate the CTAB foam
column decay. In both set-ups the foam/froth structures were monitored with an
ELMO charged coupled device (CCD). The CCD was connected to a personal
computer equipped with frame grabber, which captured and digitised the images.
The following conclusions can be drawn from the experimental results:
The machine vision system can differentiate accurately between
surfactant groups of different concentration and thus groups with unique
characteristics.
11 The stability of foam is highly correlated with all other foam variables
extracted from the image analysis system. In particular, the movement of
the foam/froth in the flotation cell has a substantial influence on the
stability values obtained for the foam/froth. III As far as the experimental system was concerned, small quartz particles (-
75 urn) stabilised the froth, while coarser particles (75-106 urn, 106-150
urn and 150+ urn) destabilised the froth.
IV Likewise, the decay of CTAB foam in a column was non-linear and
deterministic. When observed manually, the decay of long life foams
follow the same trend as short-life foams and short-life emulsions in that a
specific decay constant can be calculated for a specific surfactant system.
V The machine vision system is a viable alternative for current stability
measurements. Firstly, no data processing need to be done to calculate a
indirect stability parameter as it computes a direct stability parameter and
secondly it also computes the bubble size distribution of the sample.
The following recommendations are made:
The experimental design of the system needs to be altered to minimise the
effect the experimental environment has on results. The possibility of a
different camera set-up must be investigated. The focus of the camera on
the foam surface needs to be accurate as the computation of the stability
value depends on the quality of the image obtained.
Il The four factors that affect the stability of a flotation froth, namely solid
concentration, particle size, particle type and particle hydrophobicity
should be investigated in the same study. There exists many conflicting
studies on this subject as many studies for different particles with a
variety of sizes, hydrophobicity and concentration are performed. One
study should be conducted where all four these factors are investigated
under the same experimental conditions.
III The method with which the image analysis system deal with fine froth
need to be addressed. In laboratory systems a typical system investigated
will show a dense foam with small bubble distributions as in the case of
CTAB. The extent to which the grouping of fine froth as one bubble
influence the instability values obtained needs to be investigated .